1. Field of Invention
The present invention relates to a method for compensating for a valve lift deviation between engines equipped with a CVVL mechanism, and more particularly, to a method for compensating for a valve lift deviation by learning the valve lift and adding a learned value so that a pressure measured by a MAP sensor and a modeled MAP value are equal to each other.
2. Description of Related Art
In a method for detecting a flow rate of intake air into a cylinder from an engine equipped with a conventional CVVL (continuous variable valve lift) mechanism, the intake air flow rate is measured by a MAF sensor 100 (see FIG. 2). It is usually necessary to perform correction because the rate of change of the intake air flow rate varies depending on a number of factors including valve overlap.
However, despite the correction, the actual air flow rate and the flow rate of intake air into the cylinder may vary by a number of factors, and this may generates a valve lift deviation between engines.
FIG. 1 illustrates the patterns of valve lift deviation of such an engine equipped with a CVVL mechanism. FIG. 1 is a graph showing the MAF amount depending on the valve lift. The valve lift is measured not directly but indirectly in accordance with an angle of a control shaft. A of FIG. 1 shows the effect of a deviation in the angle of the control shaft, B of FIG. 1 shows the effect of a valve lift deviation, and C of FIG. 1 shows the effect of a combination of factors caused by the simultaneous occurrence of the deviation in the angle of the control shaft and the valve lift deviation. The three types of deviations may occur independently, or simultaneously.
Conventionally, the development of a vehicle with an internal combustion engine has been aimed at increasing the fuel ratio and reducing exhaust gases, and has been focused on improving the efficiency of a vehicle system by reducing the load of accessories, rather than on improving the internal combustion engine. To this end, an engine with a CVVL mechanism is configured such that the pressure of a surge tank depending on the opening degree of a throttle and the intake air flow rate depending on the valve lift are controlled by two load sensors, i.e., a MAF (mass air flow) sensor and a MAP (manifold absolute pressure) sensor.
However, in order to precisely control the intake air flow rate depending on the valve lift, tolerance control is required in terms of hardware of the CVVL system so that an air flow rate deviation between a cylinder and engine of an engine system can be minimized. Moreover, there has been a demand for compensation logic against a deviation that may occur between mass-produced engines within an allowed tolerance.
The information disclosed in this Background section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.